1. Field of the Invention
The present invention relates to a polishing liquid employed in a manufacturing process for a semi-conductor device. More specifically, the present invention relates to a polishing liquid which is preferably employed to polish a barrier layer consisting mainly of a barrier metallic material and an insulating layer consisting of an insulating material, for planarizing during a process for forming wiring on a semi-conductor device.
2. Related Art
In recent years, in the development of semi-conductor devices such as semi-conductor integrated circuits (hereinafter, referred to as “LSI”), increased density and integration have been sought by reducing the thickness of wiring and creating multiple layers thereof in order to miniaturize and increase the speeds of such devices. Moreover, various types of technologies, such as chemical mechanical polishing (hereinafter, referred to as “CMP”) and the like have been employed in order to achieve this objective. CMP is an essential technology for surface planarization of processed layers, such as an inter-layer dielectric, for plug formation, for formation of embedded metal wiring, and the like. CMP performs smoothing of a substrate and eliminates excessive metallic thin films from wiring formation, and eliminates excessive barrier layer on the surface of insulating films.
A conventional method of CMP is a method in which a polishing pad is fixed to the surface of a circular polishing table (polishing platen), the surface of the polishing pad is impregnated with a polishing liquid, the surface of the substrate (wafer) is pressed onto the pad, and both the polishing platen and the wafer are rotated while a predetermined amount of pressure (polishing pressure) is applied from the backsides thereof, such that the surface of the wafer is thereby planarized via the mechanical abrasion produced therefrom.
When semi-conductor devices such as LSIs are produced, fine wiring is formed in multiple wiring layers, and a barrier metal such as of Ta, TaN, Ti or TiN is pre-formed in order to prevent diffusion of the wiring material into an inter-layer dielectric, and in order to improve adhesion of the wiring material, when forming the metal wiring, such as copper wiring, in each of these layers.
In order to form each wiring layer, in general, a CMP process on metallic film (hereinafter, referred to as “metallic film CMP”) is first performed at a single stage or at multiple stages to remove excess wiring material that has been deposited by plating or the like, and thereafter, a CMP process is carried out to remove barrier metal material (barrier metal) that has been exposed on the surface of the metallic film (hereinafter, referred to as “barrier metal CMP”). However, metallic film CMP may cause over-polishing, referred to as dishing, or cause erosion of the wiring portions.
In order to reduce such dishing, in such barrier metal CMP, which follows the metallic film CMP, a wiring layer should be formed in which level differences due to dishing, erosion, and the like are ultimately reduced by regulating the polishing rate of the metal wiring portion and the polishing rate of the barrier metal portion. Specifically, in barrier metal CMP, it is preferable that the polishing rates of the barrier metal and insulation layer are moderately high, since dishing due to over-polishing of the wiring portion and erosion resulting from dishing may occur when the polishing rates of the barrier metal and the inter-layer dielectric are relatively low when compared with to the polishing rate of the metal wiring material. Not only does this have the advantage of improving the barrier metal CMP throughput, but there is a requirement to relatively increase the polishing rates of the barrier metal and the insulation layer for the above reasons, since dishing is often caused by metallic film CMP in practice.
A metal polishing liquid employed in CMP generally includes abrasive particles (for example, aluminum oxide or silica) and an oxidizing agent (for example, hydrogen peroxide or persulfuric acid). The basic polishing mechanism is thought to be that the metal surface is oxidized with the oxidizing agent, and then the oxide film formed thereby is removed with the abrasive particles.
However, when a polishing liquid including these sorts of solid abrasive particles is used in a CMP process, problems such as polishing damage (scratching), a phenomenon in which the entire polishing surface is over-polished (thinning), a phenomenon in which the polished metallic surface is dished (dishing), and a phenomenon in which plural metallic wiring surfaces are dished due to over-polishing of the insulator placed between the metallic wiring layers (erosion), and the like, may occur.
In addition, there are cost-related problems, such as complicating a conventionally employed cleaning process for eliminating residual polishing liquid from a semi-conductor surface when a polishing liquid including solid abrasive particles is used, and such as the requirement that solid abrasive particles must be precipitated when disposing of liquid after such cleaning (waste liquid).
The following investigations have been conducted with regard to a polishing liquid including solid abrasive particles.
For example, a CMP polishing agent and a polishing method that aim to achieve a high polishing rate, with virtually no occurrence of scratching is proposed (for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-17446), a polishing composition and a polishing method for improving washability in CMP is proposed (for example, JP-A No. 2003-142435), and a polishing composition that aims to prevent agglomeration of abrasive particles is proposed (for example, JP-A No. 2000-84832).
However, even in these polishing liquids, there is still no method for achieving a high polishing rate when polishing a barrier layer, while inhibiting scratching caused by the agglomeration of solid abrasive particles.
In order to improve insulation properties of wiring, low dielectric constant substrate materials (Low-k materials) are required to be developed in the future. However, Low-k materials are easily damaged by CMP and the insulation properties thereof may be seriously deteriorated by CMP. This problem is very serious when conventional polishing methods carried out in the acidic or alkaline region are used. Thus, a polishing liquid used in the pH neutral region has also been proposed (JP-A No. 2008-78233). It is hoped that this problem can be solved through use of the neutral region because a reactions tend not to occur in the neutral region.
However, there have been no methods that achieve a practical polishing rate with neutral polishing liquids. Since reactions tend not to occur in the neutral region, it is difficult to achieve a sufficient polishing rate for a barrier material and an insulating material. Therefore, the only method for increasing a polishing rate in the neutral region has been to increase the concentration of abrasive particles. However, when the concentration of the abrasive particles is increased to, for example, about 10% by mass in order to achieve a sufficient polishing rate, although the polishing rate improves, physical damage or defects are caused in the Low-k materials.